Electric motor having a stator

ABSTRACT

A stator configured to rotate a rotor with a number of magnetic poles includes a yoke that includes a back portion and a first type and first quantity of integral teeth, and a second type and second quantity of insertable teeth coupled to the back portion. At least two coils are wound with a continuous electric wire. Each of the coils is placed around two different integral teeth to define a first winding section. At least two other coils are wound with a continuous electric wire. The other coils are placed around two different insertable teeth to define a second winding section.

RELATED APPLICATION DATA

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 10/914,462 filed Aug. 9, 2004, titled “ElectricMotor Having a Stator,” now U.S. Pat. No. ______ the entire contents ofwhich are fully incorporated herein by reference.

BACKGROUND

The invention relates to a stator for an electric motor and a method ofmanufacturing and assembling the stator.

SUMMARY

In one embodiment, the invention provides a stator that defines a statoraxis. The stator includes a yoke and a plurality of teeth. Each tooth iscoupled to the yoke and defines a first recess, a first tooth end, and asecond tooth end axially opposite the first tooth end. The first recessextends axially from the first tooth end toward the second tooth end. Afirst coil includes a first end coil and a second end coil. The firstcoil is positioned on a first of the plurality of teeth such that thefirst end coil is disposed within the first recess such that the firstend coil does not extend axially beyond the first tooth end.

In another embodiment, the invention provides a stator that includes ayoke that extends in a lengthwise direction to define a core length. Atooth includes a tooth top coupled to the yoke and a coil-receivingportion. The tooth top extends in a lengthwise direction a firstdistance substantially equal to the core length, and the coil-receivingportion extends in a lengthwise direction a second distance that isshorter than the core length. A coil is disposed around thecoil-receiving space and defines a coil length that is substantially thesame as the core length.

The invention also provides a stator configured to rotate a rotor with anumber of magnetic poles. The stator includes a yoke that has a backportion and a first type and first quantity of integral teeth. A secondtype and second quantity of insertable teeth are coupled to the backportion and at least two coils are wound with a continuous electricwire. The coils are placed around two different integral teeth to definea first winding section. At least two other coils are wound with acontinuous electric wire. The coils are placed around two differentinsertable teeth to define a second winding section.

In yet another construction, the invention provides a stator including aplurality of coils arranged to define a plurality of phase windingsconfigured to rotate a rotor with a number of magnetic poles. The statorincludes a yoke that includes a back portion and a first type and firstquantity of integral teeth. The stator also includes a second type andsecond quantity of insertable teeth coupled to the back portion. Thefirst type of teeth and the second type of teeth are arranged such thatat least one pair of adjacent teeth are of different types and the coilsplaced around the respective two adjacent teeth belong to the same phasewinding.

Other aspects and embodiments of the invention will become apparent byconsideration of the detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description particularly refers to the accompanying figuresin which:

FIG. 1 is an axial schematic view of an electric motor including astator;

FIG. 2 is a perspective view of a stator including a single-layerwinding;

FIG. 3 is a perspective view of a stator including a double-layerwinding;

FIG. 4 is a perspective view of a portion of a stator core havingattachable teeth;

FIG. 5 is an end view of an attachable tooth including a coil;

FIG. 6 is an end view of the stator of FIG. 2;

FIG. 7 is an end view of the stator of FIG. 3;

FIG. 8 is a cross-sectional view of a portion of a stator of the typeshown in FIG. 7;

FIG. 9 is an end view of a stamping arrangement for a stator laminationand a tooth lamination;

FIG. 10 is an end view of the stator of FIG. 3 including an inner liner;

FIG. 11 is an end view of the stator of FIG. 3 including a castellatedinner liner or can;

FIG. 12 is a cross-sectional view of a portion of a stator including acoil retaining clip;

FIG. 13 is a cross-sectional view of a portion of a stator including astraight tooth and a small width root;

FIG. 14 is a cross-sectional view of a portion of a stator including atooth base and a small width root;

FIG. 15 is a cross-sectional view of a portion of a stator including astraight tooth and a dovetail root;

FIG. 16 is a cross-sectional view of a portion of a stator including atooth base and a dovetail root;

FIG. 17 is a perspective view of an attachable tooth including acoil-receiving recess;

FIG. 18 is a cross-sectional view of a stator including the attachabletooth of FIG. 17;

FIG. 19 is a schematic representation of one possible winding diagram ofa 3-phase stator with twelve slots and a single-layer winding;

FIG. 20 is a schematic representation of one possible winding diagram ofa 3-phase stator with twelve slots and a double-layer winding;

FIG. 21 is a schematic representation of one possible winding diagram ofa 3-phase stator with eighteen slots and a double-layer winding;

FIG. 22 is a schematic representation of one possible winding diagramfor a multi-phase motor; and

FIG. 23 is a schematic representation of another possible windingdiagram for a multi-phase motor.

DETAILED DESCRIPTION

Before any embodiments of the invention are explained in detail, it isto be understood that the invention is not limited in its application tothe details of construction and the arrangement of components set forthin the following description or illustrated in the following figures.The invention is capable of other embodiments and of being practiced orof being carried out in various ways. Also, it is to be understood thatthe phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. The use of“including,” “comprising,” or “having” and variations thereof herein ismeant to encompass the items listed thereafter and equivalents thereofas well as additional items. Unless specified or limited otherwise, theterms “mounted,” “connected,” “supported,” and “coupled” and variationsthereof are used broadly and encompass both direct and indirectmountings, connections, supports, and couplings. Further, “connected”and “coupled” are not restricted to physical or mechanical connectionsor couplings.

As shown in the FIG. 1 a motor 10 generally includes a rotor 15 disposedwithin a stator 20. The rotor 15 is mounted on a shaft 30 that extendsaxially to provide support points and to provide a convenient shaftpower take off point. Generally, two or more bearings 35 engage therotor shaft 30 and support the rotor 15 such that it rotates about arotational axis 40. The stator 20 is generally fitted into a housing 45.The stator 20 defines a substantially cylindrical aperture, or bore 55as it is commonly referred to in the motor art, that is centered on therotational axis 40. When the rotor 15 is in its operating positionrelative to the stator 20 a small air gap is established between therotor and the stator. The air gap allows for relatively free rotation ofthe rotor 15 within the stator 20.

The frame 45, if employed, supports the stator 20. One frame 45, betterillustrated in FIG. 11, includes a plurality of empty spaces 46 near thecorners. The empty spaces 46 provide cooling passages for cooling air oranother cooling fluid. In preferred constructions, the frame 45 includesa plastic material that is injection molded or otherwise formed. Inother constructions, an extruded aluminum frame is employed. In stillother constructions, other materials and other manufacturing methods maybe employed to manufacture the frame 45.

The motor 10 illustrated in FIG. 1 is a brushless permanent magnet (PM)motor. As such, the rotor 15 includes a ferromagnetic core and permanentmagnets that define two or more magnetic poles. The stator 20 includesone or more phase windings (shown in FIGS. 2-3) that can be selectivelyenergized to produce a magnetic field. The permanent magnets of therotor 15 interact with the magnetic field of the stator 20 to produceelectromagnetic torque and rotor rotation. As one of ordinary skill willrealize, the invention is also suited for other types of motors, inaddition to the brushless permanent magnet motors illustrated herein. Assuch, the invention should not be limited to only these types of motors.Furthermore, one of ordinary skill in the art will realize that theinvention can also be applied to many types of generators. The figuresdepict a motor 10 configuration having the rotor 15 placed interior tothe stator 20. However, the invention is also applicable to motorconfigurations, typically referred to as “inside-out motors,” where therotor is exterior to the stator. In addition, the figures anddescription presented herein are directed to a stator 20 and/or a motor10. However, many of the features described and illustrated could beapplied to wound rotors. Thus, while the figures and description referto a brushless motor 10 and/or a stator 20, other applications arepossible.

FIGS. 2 and 3 illustrate two possible stators 20, 60 respectively, whichare suitable for use with the motor 10 of FIG. 1. Both of the stators20, 60 include a continuous yoke 65 or back iron that defines theoutermost surface of the stator 20, 60. The yoke 65 provides structuralsupport for many of the stator core components and also provides a flowpath for the magnetic flux within the stator 20, 60. Several integralteeth 70 extend radially inward from the yoke 65. The teeth 70 include acoil-receiving portion 75 and a tooth base 80 disposed adjacent thecylindrical bore 55. The integral teeth 70 illustrated in FIGS. 2 and 3are generally straight teeth. In other words, the width of each tooth 70at the coil-receiving portion 75 is substantially equal to the width ofthe tooth 70 at the tooth base 80.

The yoke 65 defines several tooth attachment portions 85. Each of thetooth attachment portions 85 is sized and shaped to receive anattachable tooth 90 (shown in FIG. 5). In most constructions, the numberof tooth attachment portions 85 equals the number of integral teeth 70.In these constructions, the teeth 70, 90 alternate between an integraltooth 70 and an attachable tooth 90. Thus, the two teeth immediatelyadjacent any integral tooth 70 are attachable teeth 90 and the two teethimmediately adjacent any attachable tooth 90 are integral teeth 70.

In other constructions, the tooth pattern may vary such that theintegral teeth are not necessarily positioned between attachable teeth.In addition, other combinations of winding diagrams and/or the number ofphases and poles can vary. For example, FIG. 21 illustrates a stator 60a for a 3-phase brushless PM motor with eighteen slots 95 and a sixteenpole rotor (not shown). This type of motor is discussed in U.S. Pat. No.6,133,663 fully incorporated herein by reference. The stator 60 aincludes one coil 100 around each tooth 70, 90. The coils 100 on threesuccessive teeth are connected within the same phase winding to define aphase group of coils 99. Two such phase groups of coils 99 arediametrically opposed and define a phase winding. The start (go) and theend (return) of the phase windings are denoted by the subscripts “go”and “ret”, respectively, and the polarity of the coil sides, which isdetermined by the direction in which the wire is wound, is denoted byplus (+) and minus (−) signs. In one construction, within a phase groupof three coils 99 and teeth, the central tooth is an integral tooth 70and the two adjacent teeth are attachable teeth 90. Thus, thisconstruction defines a repeating pattern of two attachable teeth 90followed by an integral tooth 70 around the periphery of the 3-phasestator 60 a. Thus, the completed stator 60 a includes twice the numberof attachable teeth 90 as integral teeth 70. In another construction,the central tooth within a phase group of three coils 99 and teeth is anattachable tooth 90 and the two adjacent teeth are integral teeth 70.Thus, this construction defines a repeating pattern of two integralteeth 70 followed by an attachable tooth 90 around the periphery of the3-phase stator 60 a. Thus, the completed stator includes twice thenumber of integral teeth 70 as attachable teeth 90. The constructionsdescribed minimize the effect of radial forces and can be used withoutadditional devices such as shaft vibration dampers.

The space between any two adjacent teeth 70, 90 defines a slot 95 thatis sized to receive one or more sides of coils 100. The coils 100, aloneor in combination with other coils 100, define phase windings that canbe energized to produce a magnetic field having a desired polarity. Thestator 20 of FIG. 2 includes single-layer windings 101. Thus, only asingle side of coil 100 is positioned within each of the slots 95. Thestator 60 of FIG. 3 includes double-layer windings 102 that include twosides of coils 100 per slot 95.

The coils 100 of FIG. 2 and FIG. 3 include an electrical conductor thatis wound around the tooth 70, 90 to which the coil 100 is attached. Forcoils 100 that attach to attachable teeth 90, the conductor is wounddirectly onto the tooth 90. An electrical insulator, not shown in thefigures, is placed between the electrical conductor of the coil 100 andthe tooth 70, 90 to which it is attached. Generally, the windingoperation on an attachable tooth 90 can be performed quickly andinexpensively using a bobbin winder as is common in the motor art. Thecoils 100 that are wound on the integral teeth 70 can be wound directlyonto the teeth 70 using a needle winder or other winder suited to thetask. Alternatively, the conductor can be wound around a dummy tooth orfixture (not shown) using a less expensive bobbin winder. The coil 100is then removed from the dummy tooth or fixture and slid onto theintegral tooth 70.

One or more coils 100 are electrically connected to define a phasewinding as discussed with regard to FIG. 21. FIGS. 19 and 20 showexample winding diagrams that illustrate the coil connections withineach phase, for a 3-phase stator with twelve slots. A stator 20 a with asingle-layer winding as illustrated in FIG. 19 can be used incombination with an eight pole permanent magnet rotor to define abrushless permanent magnet (PM) motor, which can be of the DC or ACtype. A stator 60 b with a double layer winding as illustrated in FIG.20 can be used in combination with an eight pole permanent magnet rotoror, alternatively, with a sixteen pole permanent magnet rotor, to definea brushless PM motor, which can be of the DC or AC type.

In a symmetrical multi-phase stator construction, coils placed aroundthe teeth 70, 90 are connected within each phase such that the axes ofthe phase windings are equidistantly spaced around the statorcircumference. To minimize the undesirable radial magnetic forces andmagnetic pull, the stator is constructed such that diametrically opposedteeth 70, 90 have the same profile and either carry no coils or carry acoil 100 belonging to the same phase winding. The coil 100 is designedand connected such that when an electric current flows through the wire,the armature reaction magnetic field established in the respective tooth70, 90 is of equal magnitude and opposite direction to the armaturereaction magnetic field established in the diametrically opposite tooth70, 90. The armature reaction field is schematically represented by anarrow 102 in FIGS. 19-20 for the teeth 70, 90 surrounded by the coils100 of the phase winding. The stators 20 a, 60 b shown in FIGS. 19-20include an alternating pattern of integral teeth 70 and attachable teeth90, the number of integral teeth 70 and attachable teeth 90 being equal.

The integral teeth 70 are generally straight teeth. As such, each tooth70 defines a tooth profile that is substantially rectangular that allowscoils 100 to slide onto the integral tooth 70. The attachable teeth 90,better illustrated in FIG. 5, include an enlarged tooth base 105 and atooth top 110 or tooth root. The enlarged tooth base 105 makes theattachable tooth profile different from the integral tooth profile. Theenlarged tooth base 105 aids in retaining the coil 100 in the desiredposition on the tooth 90 and also aids in spreading the magnetic fieldto reduce motor cogging and torque ripple. The enlarged tooth base 105also reduces the equivalent magnetic length of the air-gap between thestator 20 and the rotor 15 and hence increases the motor specific torqueoutput. In preferred constructions, the coil-receiving portions 75 ofthe integral teeth 70 as well as the attachable teeth 90 are ofsubstantially equal width. Thus, identical coils 100, with the samenumber of turns and wire size, can be wound onto each tooth if desired.Of course, different width coil-receiving portions could be employed ifdesired. For example, the width of the integral teeth 70 and attachableteeth 90 under the winding portion may vary such that they define aratio of tooth widths between about 0.75 and 1.25.

FIGS. 4 and 5 illustrate one possible configuration of the toothattachment portions 85 and the tooth tops 110. In this construction, thetooth attachment portions 85 include a recess shaped to resemble adovetail slot. The tooth tops 110 are shaped to resemble a male dovetailroot that can mate with the female dovetail slot defined by theattachment portions 85. To achieve the desired degree of fit, it isgenerally necessary to provide an interference or shrink fit between thedovetail slot and the dovetail. The tight fit assures good contactbetween the components and minimizes the magnetomotive force (mmf) dropas the magnetic field crosses the interface between the attachable teeth90 and the yoke 65.

While a dovetail fit has been illustrated, one of ordinary skill in theart will realize that there are many other fits and configurations thatcould be used to attach the attachable teeth 90 to the yoke 65. Forexample, the dovetail fit just described could be reversed such that themale portion of the fit is formed as part of the yoke 65 and the femaleportion is formed as part of the attachable tooth 90. In still otherconstructions, different fit shapes are employed. One such shape isillustrated and described with regard to FIGS. 13-14. Still other shapesthat could be employed include, but are not limited to, T-roots, firtree roots, L-roots, and the like. Of course, the male portion of any ofthese roots could be positioned on either the yoke 65 or the attachabletooth 90 as desired.

As illustrated in FIGS. 6 and 7, each of the integral teeth 70 andattachable teeth 90 includes at least one dummy groove 115 in thesurface adjacent the stator bore 55. The dummy grooves 115 divide theteeth 70, 90 into alternating high spots 120 and low spots 125 (shown inFIGS. 8 and 9). With a single dummy groove 115, each tooth 70, 90 isdivided into two high spots 120 and one low spot 125. Thus, acastellated pattern is established around the perimeter of the statorbore 55 and the magnetic permeance of the air-gap is modified such as toeffectively reduce cogging, torque ripple, and electromagnetic noise.

FIG. 8 illustrates another construction in which each integral tooth 70includes a single dummy groove 115 and each attachable tooth 90 includesthree dummy grooves 115. Thus, the integral teeth 70 define two highspots 120 and one low spot 125, while the attachable teeth 90 definefour high spots 120 and three low spots 125. Each slot opening 130between adjacent teeth 70, 90 functions effectively as a low spot 125.Thus, a consistent pattern of substantially equal circumferential lengthalternating high spots 120 and low spots 125 extends around theperimeter of the stator bore 55. This arrangement produces relativelysmooth rotor operation and further reduces cogging and torque ripplewhen compared to the constructions of FIGS. 6 and 7. The total number ofhigh spots 120 and low spots 125 is selected in relationship with themotor polarity, number of slots and windings, and rotor to stator axialmagnetic skew. Non-uniform spatial distributions of the high spots 120and low spots 125 around the stator bore 55 are also possible, so that,under the local non-linear magnetic saturation of the tooth tops 110,the magnetic field is distributed as to improve motor performance.

The wide tooth base 105 of the attachable teeth 90 reduces the width ofthe slot opening 130 and spreads the magnetic field towards the motorair-gap. Again, this can improve motor operation, by reducingelectromagnetic noise, cogging, and torque ripple as well as increasingmotor specific output torque. Also, the use of attachable teeth 90facilitates winding with a very high copper fill factor so that thespace in a slot 95 between two adjacent coils 100 of a double-layerwinding 102 (FIG. 8) or, in the case of single-layer windings 101 (FIG.6), the space between the coil 100 and an integral tooth 70 (FIGS.15-16) is reduced. The high fill factor results in reduced windingresistance and copper losses and hence increased motor efficiency.

In most constructions, stacking a plurality of laminations 135 forms theyoke 65, including the integral teeth 70 and the tooth attachmentportions 85. The laminations 135 are generally stamped from electricalgrade steel. Similarly, stacking a plurality of tooth laminations 140generally forms the attachable teeth 90. FIG. 9 illustrates one possiblelayout arrangement for a stamping that includes both a yoke lamination135 and an attachable tooth lamination 140. The attachable toothlamination 140 is positioned within the space between adjacent integralteeth 70 and does not extend beyond the stator inner diameter. Thecenter portion of the stamping is also used for any rotor corelaminations that may be needed. Thus, the arrangement of FIG. 9 reducesthe amount of waste material and reduces the number of manufacturingsteps needed to form the laminations 135, 140. As one of ordinary skillwill realize, FIG. 9 illustrates only one attachable tooth lamination140. However, it should be understood that an attachable toothlamination 140 could be punched from the space between any two adjacentintegral teeth 70. It should also be noted that the manufacturingprocess has been described as including a punching operation. However,one of ordinary skill will realize that other manufacturing processescould be employed to cut the laminations (e.g., laser cutting, wire EDM,water-jet cutting, and the like).

In other constructions, a single piece of material forms the yoke 65,integral teeth 70 and tooth attachment areas 85. In these constructions,a compacting and/or sintering process or other suitable process is usedto form a compacted powder of ferromagnetic steel or soft magneticcomposites into the desired component. In addition, other constructionsmay include attachable teeth 90 formed from one piece of material suchas compacted powder of ferromagnetic steel or soft magnetic composites.

The use of attachable teeth 90 also allows for stators 20, 60 thatinclude a yoke 65 and integral teeth 70 manufactured from one material(e.g., laminated electric steel, powdered metal, soft magneticcomposites, solid metal, etc.) and attachable teeth 90 made from thesame material, or a different material. For example, one constructionmay include a yoke 65 and integral teeth 70 made from laminations ofelectric steel, and attachable teeth 90 made from a soft magneticcomposite. The different materials provide different electrical andmagnetic characteristics that may be used to improve the particularperformance characteristics of the motor 10.

FIG. 10 illustrates a stator 60 that includes an inner liner 145 or can.The inner liner 145 is a substantially cylindrical component that fitswithin the stator bore 55 and contacts the tooth bases of the teeth 70,90. The liner 145 includes a central opening 150 that allows for thefree passage of the rotor 15. The liner can be made of a non-magneticmaterial, such as plastic or stainless steel. In other constructions,the liner can be made of ferromagnetic material, such as magnetic steel,and designed such that the local saturation caused by the magnetic fieldwill reduce the cogging and ripple torque and/or improve the specifictorque output. In some constructions, the liner 145 may provideadditional structural support to the stator 20 by at least partiallysupporting the attachable teeth 90. In addition, the liner 145substantially separates the components of the stator 20 from those ofthe rotor 15. This can be useful in hermetically sealed motorapplications or other applications where dirt or other undesirablesubstances can enter the stator 20 via the stator bore 55.

The liner 145 illustrated in FIG. 10 is substantially tubular. As such,the perimeters of the inner surface and the outer surfaces aresubstantially circular. The tubular shape does not allow the liner 145to engage the teeth 70, 90 in any way other than friction between theteeth 70, 90 and the liner 145. As such, the liner 145 only appliesradial forces to the teeth 70, 90. While the inner liner 145 isillustrated on a stator 60 having a double-layer winding 102, it isequally applicable to stators 20 that employ single-layer windings 101.

FIG. 11 illustrates a castellated liner 155 or can disposed within astator 60 having a double-layer winding 102. The castellated liner 155includes alternating high spots 160 and low spots 165 that correspondwith the alternating high spots 120 and low spots 125 in the teeth 70,90. The alternating high spots 160 and low spots 165 interlock with thecorresponding high spots 120 and low spots 125 of the teeth 70, 90 suchthat the castellated liner 155 may provide structural support to theattachable teeth 90 in directions other than radial. Thus, thecastellated liner 155 aids in maintaining the spacing between the teeth70, 90 by locking each tooth 70, 90 into a particular location definedby the liner 155. Like the tubular liner 145, the castellated liner 155can be used on stators 20 that include either single-layer windings 101or double-layer windings 102. It should be noted that the castellatedliner 155 is illustrated as having a smooth or cylindrical innersurface. However, other constructions may include a castellated liner155 that includes a castellated inner surface that corresponds with theouter surface. The actual arrangement of the inner surface is of littleimportance to the function of the motor.

As discussed with regard to FIGS. 2 and 3, the coils 100 that surroundthe integral teeth 70 can preferably be wound onto a dummy tooth orother fixture, or on a bobbin support made of electrically-insulatingmaterial and then slid onto the actual integral tooth 70. While manydifferent systems can be used to secure the coil 100 to the tooth 70(e.g., adhesive, epoxy, injection-molded plastic, and the like), FIG. 12illustrates a construction that employs a retaining clip 170. The clip170 engages a small slot 175 that is formed in the tooth 70 to inhibitmovement of the coil 100, which is sandwiched between the clip 170 andthe yoke 65. Generally, the clip 170 is manufactured from a relativelystiff material such as spring steel such that it remains in the slot 175during motor operation. In other constructions, other mechanical meanssuch as fiberglass wedges, pins, screws, bolts, and the like are used tohold the coil 100 in the desired operating position.

In another construction, after completely assembling all the coils 100,plastic, thermoplastic resin, epoxy, or other suitable material isinjected into the spaces between the teeth 70, 90. This injectedmaterial aids in holding the coils 100 in their operating positions andcan also facilitate heat transfer from the tooth areas of the stator 20to the yoke 65. In addition, the injected material fills the emptyspaces, thus making it more difficult for dirt or other unwantedcomponents to enter and damage the stator 20. This construction can alsoinclude, as a permanent attachment or as a temporary fixture for theinjection operation, an inner liner 145 or a castellated liner 155.

FIGS. 13-16 illustrate several arrangements of attachable teethpositioned within the stator 20 that includes the single-layer winding101. FIG. 13 illustrates a tooth 180 that includes a narrow tooth top185 engaged with the stator yoke 65 and a narrow tooth base 190 adjacentthe stator bore 55. FIG. 15 illustrates another tooth 195 that includesa wide tooth top 200 that engages the yoke 65 and a narrow tooth base205. Due to the specific magnetic flux pattern during motor operation,the constructions of FIGS. 13 and 15 can be manufactured using separatedteeth laminations punched out of anisotropic magnetic material with thetooth 180, 195 oriented along the preferred magnetization (or the “easy”rolling) direction. One possible magnetic material would be electriclamination steel with an oriented grain, which is commonly employed inthe manufacture of the magnetic circuit of transformers. This choice ofmaterial reduces the magnetic circuit reluctance and the iron losses andimproves motor performance. No dummy notches are shown in FIGS. 13-16,but it is understood that, if desired they can be employed similarly tothe constructions shown in FIG. 8.

The tooth 210 illustrated in FIG. 14 includes a tooth top 215 that issimilar to the tooth top 185 of FIG. 13. The tooth 220 illustrated inFIG. 16 includes a tooth top 225 that is similar to the tooth top 200 ofFIG. 15. However, the attachable teeth 210, 220 of FIGS. 14 and 16include an enlarged tooth base 230 when compared to the attachable teeth180, 195 of FIGS. 13 and 15. The constructions with an enlarged toothbase 230, due to their specific magnetic flux pattern during motoroperation, are best suited for use with isotropic non-grain orientedmagnetic material (e.g. the electric steel commonly employed in themanufacture of the magnetic circuit of rotating electrical machines).Therefore, these constructions can not take advantage of the benefitsprovided by the use of an anisotropic grain oriented magnetic material.Furthermore, the construction of FIG. 14 has the disadvantage that thetooth 210 has to support, through the base 230, the weight of the coil100, while the profile of the tooth top 215 does not provide enhancedmechanical support, as does for example the profile of the tooth top 225in the construction of FIG. 16. On the other hand, in comparison withthe construction of FIG. 14, the construction of FIG. 16 has thedisadvantage that the coil 100 needs to be wound directly on the tooth220, using more expensive winding equipment.

Another construction of a portion of an attachable tooth 235 isillustrated in FIGS. 17 and 18. The portion of the tooth 235 includes atooth top 240, a tooth base 245, and a coil-receiving portion 250. Theportion of the tooth 235 also includes a recess portion 255 adjacent oneend of the portion of the tooth 235. In many constructions, stacking aplurality of laminations on top of one another and bonding or otherwiseattaching them forms the portion of the tooth 235. In otherconstructions, compacted powder of ferromagnetic steel, soft magneticcomposites, or other materials are used to form the portion of the tooth235. In constructions formed from laminations, a first group oflaminations having a first profile are stacked to define the portion ofthe tooth 235 that includes the tooth top 240, the tooth base 245, andthe coil-receiving portion 250. Once the coil-receiving portion 250 iscomplete, laminations having a tooth top profile and a tooth baseprofile are added to complete the tooth 235.

Two portions of an attachable tooth 235 are attached to one another tocomplete a tooth 256. In one construction, an adhesive is used to attachthe two halves of the tooth 235 and complete the tooth 256. In otherconstructions, fasteners, pins, or other attachment means are used toattach the two halves of the tooth 235 to complete the attachable tooth256.

While the construction illustrated in FIG. 17 includes two halves 235with each including one recess 255 at one end of the tooth half 235,other constructions may include a recess 255 at both ends of a singletooth. The recess 255, or recesses, provides a space for an end coil 260as illustrated in FIG. 18. Thus, with the coil 100 positioned around thetooth 235, the end coils 260 do not extend significantly beyond the endsthe tooth top 240 or the tooth base 245.

The construction of FIGS. 17 and 18 has several advantages over currentmotor constructions. For example, the recesses 255 in the teeth 235provide space for the end coils 260 and the tooth base 245 enhances theaxial coverage of the rotor by the stator 20, resulting in a morecompact motor having a higher power output per unit length than priormotors. In addition, heat from the end coils 260 is more easilytransferred to the yoke 65 and dissipated.

To assemble the stator 20 of the motor 10, the laminations 135, 140 thatmake up the various core components are first formed. As discussed withregard to FIG. 9, stamped laminations 135, 140 are one way of formingthe yoke laminations 135 and the attachable tooth laminations 140simultaneously, with other methods being possible. The yoke laminations135 are stacked on top of one another until the stack reaches a desiredaxial length. In some constructions, additional laminations, or endpieces (not shown) are positioned on the ends of the stack to completethe yoke 65 and/or the integral teeth 70. In constructions that employend pieces, the end pieces are generally of a different profile than thelaminations 135 and provide additional structural strength. Like theyoke laminations 135, the tooth laminations 140 are also stacked andbonded to one another. Once stacked, the laminations 140 define one ormore attachable teeth 90.

In constructions in which a double-layer winding 102 is desired, aconductor is wound around the required integral teeth 70 to define acoil 100. As discussed, a winding process (e.g., needle winder) that iswell known in the motor art may be used for this purpose. Preferably,the coil 100 is wound on a fixture, a dummy tooth, or on a bobbinsupport and then slid onto the integral tooth 70. This process allowsfor the use of a bobbin winder or other winder, rather than a needlewinder. A coil 100 is also wound around the attachable teeth 90. Again,a bobbin winder is well suited to this task. In stator constructionsthat employ a single-layer winding 101, the coil 100 can be positionedon only the integral teeth 70, only the attachable teeth 90, or acombination of integral and attachable teeth 70, 90 as is required bythe particular application.

The attachable teeth 90 are positioned within the yoke 65 byinterlocking the tooth attachment portion or tooth top 110 and the toothattachment portion 85. The teeth 90 engage the yoke 65 by slidingaxially along an axis 265 that is substantially parallel to the rotationaxis 40 of the motor 10. To achieve the desired level of contact, it maybe necessary to establish an interference fit. Thus, the assemblyprocess may include differential heating and/or cooling of the yoke 65and tooth 90. For example, in one construction, the yoke 65 is heated toa temperature that is 200 degrees F. higher than the tooth 90. This canbe accomplished by heating the yoke 65 alone, or by heating the yoke 65and cooling the tooth 90. The differential heating causes expansion ofthe tooth attachment portion 85 and, if cooling is used, shrinkage ofthe tooth top 110. Once the tooth 90 is positioned as desired, thetemperatures of the components equalize and a tight shrink fit isestablished. In some constructions, the end plates are positioned afterthe attachable teeth 90 are in place. In these constructions, the endplates may partially or totally cover the tooth attachment portion 85and the tooth tops 110 to inhibit unwanted axial movement of theattachable teeth 90 relative to the yoke 65.

If used, the inner liner 145 or 155 is next positioned within the statorbore 55 and positioned as desired relative to the teeth 70, 90. Onceinstalled, plastic, epoxy, resin, or other fill materials can beinjected into the spaces between the teeth 70, 90 to better secure theteeth 70, 90 and inhibit the entry of undesirable substances into thestator 20.

The order of operations for manufacturing the stator 20 can varydepending on specific motor design particularities. For example, a motordesign with very small slot openings 130, which are not size limited inrelation to the width of the coils 100 and of the teeth 70 and 90, canbe produced by first attaching coils 100 to the integral teeth 70 andthen attaching the attachable teeth 90 including their coils 100 to theyoke 65.

The concepts discussed with reference to FIGS. 19-21 can be employed toproduce stators with different combinations of teeth and windingpatterns, which are suitable for interaction with rotors of differentmagnetic polarity. For example, FIGS. 22-23 are winding diagrams for apoly-phase (three-phase) winding with each phase including multiple coilsections (two in FIG. 22). One or more coils 500 are electricallyconnected to define a winding section of a phase winding. In preferredconstructions, the coils 500 from one winding section are connectedthrough at least one continuous electric wire, which is also wound toproduce the coils 500. For example, in FIG. 22, the two coils 601 and602 define one winding section of the red (R) phase which are wound andconnected with the electric wire 701. Other types of connections, knownto those skilled in the art, such as wire soldering or wire connectionthrough an electrical connector can also be employed if desired.

FIG. 22 illustrates the winding sections, one per each phase, associatedwith the coils 500 that are wound (placed) around the insertable(attachable) teeth 90. FIG. 23 shows all the coils 500 of the windingand only the connections for the winding sections associated with thecoils attached (inserted on) to the integral teeth 70. The connectionsfor the other winding sections are shown in FIG. 22. Some of the slots515 include two sharing coil sides that belong to different coilsections. Some of the slots 520 include coils that are part of differentphase windings, while other slots 525 include coils that are part of thesame phase winding. In the slots in which the coils 500 are part of thesame phase winding, the two coil sides have the same polarity. Thedescribed winding arrangement is preferable, as the coils 500 aregrouped corresponding to their manufacturing technology and theconnections within a winding section are simplified. Before connectionto a power supply, the terminals of the phase winding sections may beinterconnected. For example, for a series connection per phase, terminalR1go is connected to one of the power supply terminals, terminal R1retis connected to terminal R2go and terminal R2ret is connected to anotherterminal of the power supply.

A three-phase stator as that exemplified in FIGS. 22-23 can be used incooperation with a PM rotor to define a brushless PM motor. The polarityof a brushless PM motor is determined by the magnetic polarity of therotor. Ten-pole rotors, as well as fourteen-pole rotors are suitable foroperation with a 12-tooth stator core with the winding pattern of FIG.23. The total number of stator teeth (integral plus insertable) is equalto the number of rotor magnetic poles plus two and the number of rotormagnetic poles minus two, respectively. Other combinations of stator androtor polarities, known to those skilled in the art, such as the numberof stator teeth being equal to the rotor polarity plus or minus one, arealso possible. For the stators shown in FIGS. 19-20 possible rotorpolarities are eight and sixteen, so that the total number of teeth(integral plus insertable) is equal to the number of poles times thenumber of phases and divided by two and four, respectively.

A stator with insertable teeth 90 and integral teeth 70 can also bewound for single or two phase operation. For convenience, one windingsection is wound around at least some of the attachable teeth 90 andanother winding section is wound around at least some of the integralteeth 70. In the preferred construction, the number of insertable teeth90 is equal to the number of integral teeth 70, the position of the twotypes of teeth 70, 90 is alternating around the circumference, one ofthe winding sections is wound around all of the attachable teeth 90 andthe other winding section is wound around all of the integral teeth 70.For a single-phase motor, before connection to the power supply, the twowinding sections are electrically connected in series or parallel todefine a single phase winding. In the motor slots that include two coilsides, both have the same polarity. In order to define a brushless PMmotor, a single-phase stator as previously described is used inconjunction with a PM rotor so that the total number of stator teeth(integral plus insertable) is equal to the rotor polarity.

For a two-phase motor, with the phases spatially shifted by 90electrical degrees, a winding section wound around at least some of theattachable teeth 90 is used to define a first phase, and a secondwinding section, which is wound around at least some of the integralteeth 70, is used to define a second phase. In order to define abrushless PM motor, a two-phase stator as previously described is usedin conjunction with a PM rotor so that the total number of stator teeth(integral plus insertable) is equal to twice the rotor polarity.

For a two-phase motor, with the phase spatially shifted by 180 degrees,a motor also commonly referred to as uni-polar single-phase motor, awinding section wound around at least some of the attachable teeth isused to define a first phase and a second winding section, which iswound around at least some of the integral teeth, is used to define asecond phase. In order to define a brushless PM motor, a two-phasestator as previously described is used in conjunction with a PM rotor sothat the total number of stator teeth (integral plus insertable) isequal to the rotor polarity.

As mentioned previously, the stator according to the invention can beapplied for other types of electrical machines, such as, for example,a.c. synchronous or asynchronous (induction) motors and generators. Inan induction motor with a squirrel cage rotor, the polarity of themachine and of the rotor is determined by the polarity of thefundamental wave of the stator magnetomotive force (or of the harmonicwave with the largest magnitude), which can be calculated based on thedistribution (pattern) of the stator winding through methods known tothose skilled in the art.

The examples from FIGS. 19-23 show the insertable teeth 90 as havingsubstantially the same width as the integral teeth 70 and the insertableteeth 90 having an enlarged tooth base. Variations, apart from thoseshown in FIGS. 13-16 are possible. For example, for the construction ofFIG. 21, especially when used in a brushless PM motor, the integralteeth 70 can be thinner or wider than the attachable teeth 90, dependingon the design objective. The constructions of FIGS. 22-23 can be builtwith all of the insertable and integral teeth 70, 90 havingsubstantially the same tooth base profile (shape) in order to minimizethe parasitic (harmonic) torques and forces, especially when used in abrushless PM motor of the poly-phase type. However, the constructionsdescribed have in common, among other things, the fact that at leastsome of the teeth are insertable in order to allow an increase of theslot-fill factor and enhance motor performance.

Thus, the invention provides, among other things, a new and usefulstator 20 for an electric motor 10 and method of assembling the stator20. The new stator 20 has improved electromagnetic and mechanicalperformance and enhanced manufacturability. The constructions of thestator 20 and the methods of assembling the stator 20 described aboveand illustrated in the figures are presented by way of example only andare not intended as a limitation upon the concepts and principles of theinvention. Various features and advantages of the invention are setforth in the following claims.

1. A stator defining a stator axis, the stator comprising: a yoke; aplurality of teeth, each tooth coupled to the yoke and defining a firstrecess, a first tooth end, and a second tooth end axially opposite thefirst tooth end, the first recess extending axially from the first toothend toward the second tooth end; and a first coil including a first endcoil and a second end coil, the first coil positioned on a first of theplurality of teeth such that the first end coil is disposed within thefirst recess such that the first end coil does not extend axially beyondthe first tooth end.
 2. A stator as set forth in claim 1 wherein eachtooth includes a second recess extending axially from the second toothend toward the first tooth end.
 3. A stator as set forth in claim 2wherein the second end coil is disposed within the second recess suchthat the second end coil does not extend axially beyond the second toothend.
 4. A stator as set forth in claim 1 wherein each of the pluralityof teeth includes a powdered metal portion.
 5. A stator as set forth inclaim 1 wherein each of the plurality of teeth includes a first portionand a second portion separate from the first portion, each of the firstportion and the second portion formed from a powdered metal.
 6. A statoras set forth in claim 1 wherein the first coil is disposed around onlythe first tooth.
 7. A stator as set forth in claim 1 wherein the yoke isformed from a plurality of laminations stacked in a stackwise directionand at least one of the plurality of teeth is formed from a powderedmetal.
 8. A stator as set forth in claim 1 wherein the plurality ofteeth cooperate to define eighteen slots.
 9. A stator as set forth inclaim 1 wherein at least a portion of the plurality of teeth are formedseparate from the yoke.
 10. A stator comprising: a yoke extending in alengthwise direction to define a core length; a tooth including a toothtop coupled to the yoke and a coil-receiving portion, the tooth topextending in a lengthwise direction a first distance substantially equalto the core length, and the coil-receiving portion extending in alengthwise direction a second distance that is shorter than the corelength; and a coil disposed around the coil-receiving space and defininga coil length that is substantially the same as the core length.
 11. Thestator of claim 10, wherein the yoke includes a plurality of laminationsstacked in the lengthwise direction and the tooth is formed from apowdered metal.
 12. The stator of claim 10, wherein the tooth is a firstof a first quantity of teeth, each tooth formed separate from the yokeand coupled to the yoke.
 13. The stator of claim 12, further comprisinga second quantity of teeth integrally-formed as part of the yoke. 14.The stator of claim 13, wherein the first quantity is twice the secondquantity.
 15. The stator of claim 13, wherein the first quantity ofteeth and the second quantity of teeth cooperate to define eighteenslots therebetween.
 16. The stator of claim 10, wherein the toothincludes a first tooth portion formed separate from a second toothportion, the first tooth portion and second tooth portion cooperating tocompletely define the tooth.
 17. A stator configured to rotate a rotorwith a number of magnetic poles, the stator comprising: a yoke thatincludes a back portion and a first type and first quantity of integralteeth; a second type and second quantity of insertable teeth coupled tothe back portion; at least two coils wound with a continuous electricwire, each of the coils being placed around two different integral teethto define a first winding section; and at least two other coils woundwith a continuous electric wire, the other coils being placed around twodifferent insertable teeth to define a second winding section.
 18. Thestator of claim 17, wherein the two winding sections belong to the samephase winding.
 19. The stator of claim 18, wherein one slot includes twocoil sides sharing the slot, each of the two coil sides belonging to adifferent winding section and the two coil sides having the samepolarity.
 20. The stator of claim 19, wherein the quantity of integralteeth plus the quantity of insertable teeth is equal to the number ofmagnetic poles.
 21. The stator of claim 17, wherein the two windingsections each belong to a different phase winding.
 22. The stator ofclaim 21, wherein the quantity of integral teeth plus the quantity ofinsertable teeth is equal to the number of magnetic poles.
 23. Thestator of claim 21, wherein the quantity of integral teeth plus thequantity of insertable teeth is equal to twice the number of magneticpoles.
 24. The stator of claim 21, wherein the quantity of integralteeth plus the quantity of insertable teeth is equal to the number ofmagnetic poles times the number of stator phases divided by two.
 25. Thestator of claim 21, wherein the quantity of integral teeth plus thequantity of insertable teeth is equal to the number of magnetic polestimes the number of stator phases divided by four.
 26. The stator ofclaim 17, wherein the number of poles equals sixteen and the number ofslots equals eighteen.
 27. The stator of claim 17, wherein the number ofpoles equals ten and the number of slots equals twelve.
 28. The statorof claim 17, wherein the first quantity of integral teeth equals thesecond quantity of insertable teeth.
 29. The stator of claim 17, furthercomprising a liner positioned between the stator and the rotor.
 30. Thestator of claim 17, wherein the yoke defines a first axial length andthe insertable teeth define a second axial length that is shorter thanthe first axial length.
 31. The stator of claim 17, wherein eachinsertable tooth is disposed between two integral teeth, and eachintegral tooth is positioned between two insertable teeth.
 32. A statorincluding a plurality of coils arranged to define a plurality of phasewindings configured to rotate a rotor with a number of magnetic poles,the stator comprising: a yoke that includes a back portion and a firsttype and first quantity of integral teeth; and a second type and secondquantity of insertable teeth coupled to the back portion, the first typeof teeth and the second type of teeth arranged such that at least onepair of adjacent teeth are of different types and the coils placedaround the respective two adjacent teeth belong to the same phasewinding.
 33. The stator of claim 32, wherein the quantity of integralteeth is equal to the quantity of insertable teeth.
 34. The stator ofclaim 32, wherein the quantity of integral teeth is half the quantity ofinsertable teeth.
 35. The stator of claim 32, wherein the quantity ofintegral teeth plus the quantity of insertable teeth is greater than orequal to the number of magnetic poles minus two.
 36. The stator of claim35, wherein the quantity of integral teeth plus the quantity ofinsertable teeth is equal to the number of magnetic poles minus two. 37.The stator of claim 32, wherein a second pair of adjacent teeth havecoils that belong to different phase windings.
 38. The stator of claim37, wherein the pair of adjacent teeth define a first slot and whereinthe polarity of the coil on each of the teeth of the pair of adjacentteeth within the first slot is the same, and the second pair of adjacentteeth define a second slot and wherein the polarity of the coil on eachof the teeth of the second pair of teeth within the second slot areopposite.
 39. The stator of claim 32, wherein the pair of adjacent teethdefine a slot and wherein the polarity of the coil on each of the teethwithin the slot is the same.
 40. The stator of claim 32, wherein thequantity of integral teeth plus the quantity of insertable teeth is lessthan or equal to the number of magnetic poles plus two.
 41. The statorof claim 40, wherein the quantity of integral teeth plus the quantity ofinsertable teeth is equal to the number of magnetic poles plus two. 42.The stator of claim 32, wherein the number of poles equals sixteen andthe number of slots equals eighteen.
 43. The stator of claim 32, whereinthe number of poles equals ten and the number of slots equals twelve.44. The stator of claim 32, further comprising a liner positionedbetween the stator and the rotor.
 45. The stator of claim 32, whereinthe yoke defines a first axial length and the insertable teeth define asecond axial length that is shorter than the first axial length.
 46. Thestator of claim 32, wherein the insertable teeth include a firstcoil-receiving portion having a first substantially constant width andthe integral teeth define a second coil-receiving portion having asecond substantially constant width that is different than the firstwidth.